The submerged portions of the ships and marine structures are provided with an antifouling coating containing rosin or organic tin for the purpose of preventing corrosion or the drop of cruising speed of the ships due to attachment of marine creatures such as barnacles, teredos, and algae. Such an antifouling coating is also provided on the nets used at the nurseries of fishes or marine products for the purpose of preventing fatal effect on the reared fishes and shellfishes by the attachment of marine organisms on the nets.
The antifouling effect of these antifouling coatings is demonstrated as the rosin and antifouling substance(s) contained in the coating are eluted into seawater. Therefore, when the coating is left immersed in seawater for a long period of time, the eluting substance is gradually decreased while the non-eluting matter is left in the coating, and at the same time the coating surface becomes jagged, which tends to excessively reduce the effect of the coating to prevent attachment and accumulation of marine organisms. In the case of organotin-containing self polishing type paint, the coating surface is gradually dissolved away to constantly renew the surface so that the antifouling substance will be always kept exposed on the coating surface to allow long-time retention of its antifouling effect. This type of antifouling paint, however, has a possibility to give baneful influence to fishes and shellfishes because of strong toxicity of organic tin contained therein. Thus, request is intensifying in the industry for the development of a self polishing type antifouling paint composition which is low in toxicity and capable of exhibiting its antifouling effect in the sea for a prolonged period of time. Many studies have been made on the self polishing type paints free of organic tin. For example, JP-A-62-57464 and JP-A-62-84168 describe the antifouling paint compositions using the copolymers having a metal-containing group at the end of the side chain. Also, JP-A-5-171066 discloses an antifouling paint composition containing a copolymer comprising a metal-containing monomer having 2 to 3 double bonds, as a vehicle.
However, the antifouling paints using metal-containing copolymers such as described in JP-A-62-57464 and JP-A-62-84168 mentioned above are reduced in their self polishing action with time, so that their antifouling effect can hardly last for a long period of time. If the metal content per polymer molecular weight is increased for improving the self polishing characteristics of these antifouling paints, the formed coating becomes hard and frail and tends to develop cracks or exfoliate.
On the other hand, the antifouling paint using a copolymer such as described in JP-A-5-171066, although capable of maintaining its self polishing action for a long period of time tends to have an insufficient rate of consumption of the coating, hence is not necessarily satisfactory in long-time antifouling effect of coating. Also, the foamed coating tends to become hard and fragil with the lapse of time, and further this type of paint is unsatisfactory in its recoatability on the old coating formed from an organotin-based paint and so on, so that the recoating film tends to crack or exfoliate.